Earth's mantle
[8][9] The upper mantle is dominantly peridotite, composed primarily of variable proportions of the minerals olivine, clinopyroxene, orthopyroxene, and an aluminous phase.
[14] The lower mantle is composed primarily of bridgmanite and ferropericlase, with minor amounts of calcium perovskite, calcium-ferrite structured oxide, and stishovite.
Rare exposures of mantle rocks occur in ophiolites, where sections of oceanic lithosphere have been obducted onto a continent.
The volcanism often attributed to deep mantle plumes is alternatively explained by passive extension of the crust, permitting magma to leak to the surface: the plate hypothesis.
[24] The convection of the Earth's mantle is a chaotic process (in the sense of fluid dynamics), which is thought to be an integral part of the motion of plates.
The observed continental drift is a complicated relationship between the forces causing oceanic lithosphere to sink and the movements within Earth's mantle.
[26] D″ may consist of material from subducted slabs that descended and came to rest at the core–mantle boundary or from a new mineral polymorph discovered in perovskite called post-perovskite.
Earthquakes at shallow depths are a result of faulting; however, below about 50 km (30 mi) the hot, high pressure conditions ought to inhibit further seismicity.
Estimates for the viscosity of the upper mantle range between 1019 and 1024 Pa·s, depending on depth,[25] temperature, composition, state of stress, and numerous other factors.
However, when large forces are applied to the uppermost mantle it can become weaker, and this effect is thought to be important in allowing the formation of tectonic plate boundaries.
Coordinated by Scripps Institution of Oceanography at the University of California, San Diego, DSDP provided crucial data to support the seafloor spreading hypothesis and helped to prove the theory of plate tectonics.
[30] On 5 March 2007, a team of scientists on board the RRS James Cook embarked on a voyage to an area of the Atlantic seafloor where the mantle lies exposed without any crust covering, midway between the Cape Verde Islands and the Caribbean Sea.
A novel method of exploring the uppermost few hundred kilometres of the Earth was proposed in 2005, consisting of a small, dense, heat-generating probe which melts its way down through the crust and mantle while its position and progress are tracked by acoustic signals generated in the rocks.
[34] The probe consists of an outer sphere of tungsten about one metre in diameter with a cobalt-60 interior acting as a radioactive heat source.
In 2009, a supercomputer application provided new insight into the distribution of mineral deposits, especially isotopes of iron, from when the mantle developed 4.5 billion years ago.
[36] In 2023, JOIDES Resolution recovered cores of what appeared to be rock from the upper mantle after drilling only a few hundred meters into the Atlantis Massif.
[37] In January 2025, scientists reported discovering two supercontinents–one beneath Africa, the other under the Pacific Ocean–of unmixed regions lingering in the mantle.
